Cyclic aromatic compounds have recently received attention, because of the characteristics derived from their cyclic conformation, i.e., their structure-derived specificity. More specifically, the cyclic aromatic compounds have potential for development in applications of high-performance materials or functional materials and are expected to be used as inclusion compounds or to be used as monomers effective for syntheses of high molecular-weight linear polymers by ring-opening polymerization. Cyclic polyarylene sulfides (hereinafter polyarylene sulfide may be abbreviated as PAS) are remarkable compounds belonging to the category of cyclic aromatic compounds.
As a production method of cyclic polyarylene sulfide, disclosed are, for example, a method of oxidative polymerization of a diaryl disulfide compound under an ultra-dilute condition (for example, Patent Document 1) and a method of heating a copper salt of 4-bromothiophenol in quinoline an ultra-dilute condition (for example, Patent Document 2). These methods, however, require the ultra-dilute condition as essential. These methods produce cyclic polyarylene sulfide with high selectivity and suppress production of linear polyarylene sulfide to a very little amount, but requires a long time for the reaction and allows for production of only a very little amount of cyclic polyarylene sulfide per unit volume of a reaction vessel. These methods accordingly have lots of difficulties in terms of producing cyclic polyarylene sulfide with high efficiency. Another problem is difficulty in purification, so that the cyclic polyarylene sulfide obtained has low purity.
As a method of producing cyclic polyarylene sulfide by desalination condensation from versatile raw materials like a sulfidizing agent and a dihalogenated aromatic compound, disclosed is a method of controlling the amount of sodium sulfide relative to N-methylpyrrolidone to 0.1 mol/liter and performing contact reaction at a reflux temperature by addition of dichlorobenzene (for example, Non-Patent Document 1). This method employs the dilute condition that the volume of an organic polar solvent is 1.25 liters or more per 1 mol of sulfur atom of the sulfidizing agent and is thus expected to obtain cyclic polyarylene sulfide. This method, however, allows for production of only a very little amount of cyclic polyarylene sulfide. Other problems are low purity of the resulting cyclic polyarylene sulfide and a long time required for the reaction.
As a method of producing high-purity cyclic polyarylene sulfide with high yield using the similar raw materials, disclosed is a method of heating a reaction mixture including a sulfidizing agent and a dihalogenated aromatic compound at a temperature exceeding a reflux temperature under ordinary pressure by using an organic polar solvent of 1.25 liters or more relative to 1 mol of sulfur of the sulfidizing agent (for example, Patent Document 3). This method enables the consumption rate of the dihalogenated aromatic compound to reach about 90% in a relatively short time period like 0.5 to 2 hours and improves the selectivity of cyclic polyarylene sulfide to about 35%. Improvement of the selectivity, however, requires the diluter condition, so that only a little amount of cyclic polyarylene sulfide is obtained per unit volume of a reaction vessel at even the high yield. There is accordingly a need to satisfy both the yield and the production amount.
As a method proposed to solve the above problem, disclosed is a method of heating and reacting a linear polyarylene sulfide, a sulfidizing agent and a dihalogenated aromatic compound in 1.25 liters or more of an organic polar solvent per 1 mol of sulfur content included in the reaction mixture (for example, Patent Document 4). This method uses the linear polyarylene sulfide as the raw material and thereby reduces the amount of the monomer used. This accordingly improves the yield of cyclic polyarylene sulfide relative to the monomer and is expected to have industrial applicability. This method, however, still has a little amount of cyclic polyarylene sulfide obtained per volume of a reaction vessel. There is accordingly a need for improvement of the production amount.
As a similar method, disclosed is a method of heating and reacting a reaction mixture including at least a linear polyarylene sulfide, a sulfidizing agent and an organic polar solvent, adding a dihalogenated aromatic compound to the resulting reaction mixture, and further heating and reacting the resulting reaction mixture in 1.25 liters or more of the organic polar solvent per 1 mol of sulfur content included in the reaction mixture (for example, Patent Document 5). This method also uses the linear polyarylene sulfide as the raw material and thereby reduces the amount of the monomer used. This method, however, employs the multi-step reaction and requires the complicated operations including dilution of the reaction mixture and separate addition of the dihalogenated aromatic compound. This method also has a little amount of cyclic polyarylene sulfide obtained per volume of a reaction vessel. There is accordingly a need for further improvement of efficiency.
As a method of producing polyarylene sulfide, disclosed is a method of causing a monomer mixture including at least one species of sulfur source selected from alkali metal sulfides and alkali metal hydrosulfides, a dihalogenated aromatic compound and an organic polar solvent to be supplied to a polymerization line provided with a continuous tubular reactor including a static blending structure and to pass through the polymerization line during progress of polymerization (for example, Patent Document 6). This method aims to suppress the production cost of the polyarylene sulfide and does not refer to production of a cyclic polyarylene sulfide at all. Furthermore, this method uses the solvent of less than 1.25 liters per 1 mol of sulfur content of the sulfur source and is thus expected to have only a low yield even if cyclic polyarylene sulfide is produced. This method is accordingly not efficient as the production method of the cyclic polyarylene sulfide.
Patent Documents:
    Patent Document 1: JP 3200027B (claims)    Patent Document 2: U.S. Pat. No. 5,869,599 (page 14)    Patent Document 3: JP 2009-30012A (claims)    Patent Document 4: WO 2008/105438 (claims)    Patent Document 5: JP 2011-68885A (claims)    Patent Document 6: JP 2008-285596A (claims)Non-Patent Documents:    Non-Patent Document 1: Polymer, vol. 37, No. 14, p 3111-3112, 1996